Without looking at the actual recipe, in most cases, it means that the egg mixture is added to the other "hot" mixture gradually and, sometimes in small portions, and when the warmed mixture is a bit cooled. What you DO NOT want is to have the eggs scramble. It's a gentle way of incorporating eggs into a warm mixture.
"As a girl I had zero interest in the stove." - Julia Child
This is real inspiration. Look what Julia became!